Damp Proof Membrane Kit 10m²

Details

Fixing
Clean the substrate to obtain as flat a surface as possible. Remove any damaged, loose or crumbling plaster. The 3mm membrane (with the mesh facing outward) should be fixed to a firm flat surface wherever possible. Dubbing out may be necessary on uneven substrates. The 3mm membrane is fixed with the plugs to all substrates except when fixing to plywood or timber when a galvanised clout nail should be used. The 3mm membrane can be fitted horizontally or vertically. Care must be taken to ensure that the membrane is pulled tight and square while fixing as this will avoid sagging or bulging which can cause problems when plastering or rendering. Fix from the centre outward. Holes can be drilled through the membrane into the wall to a depth of at least 50mm using a 7mm or 8mm bit depending on substrate. Before inserting the plug, a squirt of mastic should be inserted in the hole to avoid any bridging of moisture through the shaft of the plug when it is fitted. If excessive pressure is applied when fixing the plugs this can distort the membrane causing indentations in the membrane. A smaller-diameter bit can be used on soft backgrounds to avoid the risk of pull-out. Fixing centres internally must not be greater than 250mm horizontally or vertically. On curved or uneven surfaces, closer fixings should be used. Ensure firm and even fixing. Fit the membrane on any return wall to a length of 300mm to avoid drawing damp from the original offending wall. Fixing should not take place in extreme conditions, above 30° and below -5°.

Fitting
The 3mm membrane can be cut with a sharp knife or scissors. Where it has to be cut around the pipes or other fixtures, the exposed area must be treated with the waterproof mastic to ensure there is no bridging between the damp or stained surface and the new finish. The membrane should be taken into reveals. Mastic sealing is recommended between new plaster and window frame edges, etc. This avoids bridging. Plaster board panels can be fixed to the membrane by the dot and dab method, giving a dry surface ready for immediate decoration. Bonding plaster can be used. ‘Dabs’ should be applied on the membrane fixing heads and membrane to cover 50% of the membrane.

Note: Although the system poses no health hazards usual protective clothing and goggles should be worn in accordance with current health and safety regulations.

Jointing
The 3mm membrane can easily be bent round corners as it is a very flexible material. Alternatively, it can be butt jointed. Likewise, butt jointing would be appropriate if the material is being used horizontally and the finish height is more than 3m. When fixing the material, ensure that the plugs are not fixed initially close to the area to be butt jointed as a strip of DPM or other waterproof material 80mm wide must be inserted before the butt joint is completed.

It is recommended that the 3mm membrane is raised from the floor by 20-25mm to prevent bridging from the floor to the wall plaster or render. Where a polythene membrane is incorporated in the floor, it should be carried in front of the membrane and tape jointed to form a seal where rising or penetrating damp is problematic. A gap can be left at ceiling height of 3mm and this can subsequently be covered by a wooden bead or coving. It would be appropriate to leave a gap at ceiling level where moisture is the predominant problem the membrane is required to overcome.

Finishing
The most popular application is plasterboard, although plywood boards and other moisture resistant boards can be used. A dot and dab method would be applicable to apply these materials using Gyproc Wall Adhesive or similar. The adhesive should be applied to the fixing heads on the membrane and dabs on the actual board to be fixed. At least 50% of the board should be covered by dabs to ensure a good bond. The board should rest on a level plinth when presented to the membrane and the bonding compound will of course key into the mesh. It may be appropriate to drive in one or two hardened fixing pins at the top and middle of the board to hold it in place while the adhesive dries. Subsequently the pins can be driven home or extracted when the fixing compound is thoroughly dry. The joints between the boards can be taped and a skim coat of plaster if desired or wallpaper or other decorative materials can be applied.

If plaster is to be applied then Tilcon Whitewall One Coat, British Gypsum Thistle Hardwall or Permagard High Impact Backing Plaster can be used. Carlite Bonding can also be applied but it does take longer to dry. All plaster finishes should be applied strictly in accordance with the manufacturer’s instructions and good plastering practice as described in BS 5492: 1990 Code of Practice for internal plastering. Always allow 24 hours drying time between coats for plaster and 7 days for sand & cement. DO NOT APPLY DECORATIONS UNTIL PLASTER IS THOROUGHLY DRY. If the finished wall is punctured when holes are drilled to fix brackets, etc., a waterproof mastic should be inserted before fixing bolts are inserted to ensure no bridging to the damp surface occurs. CAUTION: DO NOT USE LIMELIGHT, OR RENOVATING TYPE PLASTERS AS THESE CAN EXPAND ON THE MEMBRANE AND BUCKLE THE FINISH.

Sand and Cement Render
Render should be a mix of 1 lime: 1 cement: 6 clean well-graded sharp sand. To lessen the incidents of cracking which is liable to occur with any cement-based render to a smooth non-porous surfaced material such as the 3mm membrane, it is best to mix the lime and sand a day or more before use. Cement can then be added at the time of rendering. The work should be of three coats. The purpose of the scratch coat is to stiffen up the lath and to provide rough and absorbent backing for subsequent coats. Work this scratch coat well into the mesh. Subsequent coats should be of the same mix. Each coat of render should be allowed to dry for a period of not less than seven and preferably ten days, longer if possible. Cracking may occur if shorter time is allowed between coats.

NOTE: When using masonry cement, do not use lime, as these materials contain a plasticiser. All rendering should be applied in accordance with BS 5262.